The present invention relates to a method and apparatus for adjusting resistors used in a load-cell scale.
Generally, in a load-cell scale, an electrical signal corresponding to a load is generated by a load cell. The electrical signal is converted into a digital signal corresponding to the load weight by an amplifier and an A/D converting circuit having an A/D converter. The digital signal is read by a microcomputer and is converted into corresponding weight data in units of, e.g., grams. The weight data is converted into display data and is output to a display.
In a load-cell scale of this type, it is quite important to reliably set the temperature characteristics in order to improve the precision. For this purpose, in a scale manufacturing step, the resistors in the load cell and the A/D converter must be adjusted in order to adjust the temperature characteristics.
Such adjustment is conventionally performed separately in the load cell and the A/D converting section. In order to achieve a predetermined level of precision as a whole, considerably high precisions are required for the adjustments of the resistors in the load cell and the A/D converting section, resulting in a time-consuming adjustment operation. Also, since the resistors to be used must be made highly accurate, the load-cell scale is expensive. Since resistor adjustment is conventionally performed using a variable resistor, it must be performed manually, resulting in a further time-consuming adjustment operation.
In another method, a load cell and an A/D converting section are arranged close to each other and the adjustment of their temperature characteristics is performed under the same temperature conditions. With this method, however, the adjustment of the resistors must be performed manually using a variable resistor, resulting in a time-consuming operation.
In a load cell scale, resistor adjustment must be performed not only for setting temperature characteristics but also for setting a zero point or a span. The same problems as described above also arise in this case.